Method of making internally oxidized dispersion hardened copper product

ABSTRACT

A WROUGHT, DUCTILE, PRODUCT COMPRISING A COPPER MATRIX THROUGH WHICH PARTICLES OF A METAL OXIDE ARE INTIMATELY DISPERSED IS MADE BY INTERNALLY OXIDIZING AT A HIGH TEMPERATURE (PREFERABLY 1400*F. TO 1700*F.) AN ALLOY OF COPPER AND ONE OR MORE READILY OXIDIZED METALS HAVING OXIDES OF HIGH HEATS OF FORMATION. THE OXIDATION CONVERTS THE METAL ALLOYED WITH THE COPPER TO OXIDE AND SATURATES THE COPPER MATRIX WITH OXYGEN. THE OXIDIZED METAL IS HEATED (PREFERABLY AT 1400*F. TO 1700*.) IN HYDROGEN UNTIL THE OXYGEN DISSOLVED IN THE COPPER MATRIX (BUT NOT THE OXIDE OF THE METAL ALLOYED INITIALLY WITH THE COPPER) IS REDUCED, RESULTING IN SEVERE EMBRITTLEMENT OF THE METAL. THE RESULTING COPPER PRODUCT IS BROKEN UP MECHANICALLY TO GRANULAR FORM, AND THEN IS FORMED INTO AN EXTRUSION BILLET WHICH IS EXTRUDED HOT (AT SAY 1700* F. TO 1900*F.) INTO A DUCTILE, WORKABLE SHAPE OF SUITABLE CROSS SECTION. THE EXTRUDED SHAPE MAY BE COLD WORKED TO FINAL FORM.

United States Patent ()fi ice 3,552,954 METHOD OF MAKING INTERNALLYOXIDIZED DISPERSION HARDENED COPPER PRODUCT Allen S. McDonald, Jr.,Bridgeport, Conn., assignor to Handy & Harman, Fairfield, Conn., acorporation of New York No Drawing. Filed Sept. 20, 1968, Ser. No.761,335 Int. Cl. C22c 31/04 US. Cl. 75-206 14 Claims ABSTRACT OF THEDISCLOSURE A wrought, ductile, product comprising a copper matrixthrough Which particles of a metal oxide are intimately dispersed ismade by internally oxidizing at a high temperature (preferably 1400 F.to 1700 F.) an alloy of copper and one or more readily oxidized metalshaving oxides of high heats of formation. The oxidation converts themetal alloyed with the copper to oxide and saturates the copper matrixwith oxygen. The oxidized metal is heated (preferably at 1400 F. to1700" F.) in hydrogen until the oxygen dissolved in the copper matrix(but not the oxide of the metal alloyed initially with the copper) isreduced, resulting in severe embrittlement of the metal. The resultingcopper product is broken up mechanically to granular form, and then isformed into an extrusion billet which is extruded hot (at say 1700 F. to1900 F.) into a ductile, workable shape of suitable cross section. Theextruded shape may be cold worked to final form.

This invention relates to the production of an in ternally oxidizeddispersion hardened copper product comprising a matrix of metalliccopper having particles of a metal oxide intimately dispersedtherethrough. The invention is particularly directed to an improvedmethod for making such a product.

It is not practical to produce dispersion hardened copper byconventional melting and casting procedures. Such products have,however, been made by the methods of powder metallurgy, involving mixingpowders of copper and the metal oxide, compacting and sintering themixed powders, and working the sintered compact to the desiredfabricated shape.

More recently the process of the McDonald, Spooner, and Coxe US. Pat.No. 3,296,695 has been developed for internally oxidizing an alloy ofcopper (or similar metal) with a minor portion of the metal of theoxide. Briefly, this procedure involves exposing a rolled relativelythin strip of such alloy to an oxidizing environment under conditionssuch that oxygen diffuses through the strip and oxidizes the metalalloyed with the copper. The resulting internally oxidized strip iscoiled to forma cylindrical billet which is then extruded hot into ashape of desired cross section.

The present invention provides an improvement on the process of theMcDonald, Spooner and Coxe patent, in which an alloy of copper andreadily oxidized metal such as beryllium, aluminum, magnesium,zirconium, or silica, after being internally oxidized, is subjected to areducing operation in a hydrogen-containing atmosphere to eliminateexcess oxygen dissolved in the copper matrix. Such reduction severelyembrittlesthe copper. This brittle product is readily broken up intosmall particles which are canned or compacted to form an extrusionbillet.

According to the invention, therefore, a method is provided for making awrought,- ductile, dispersion hardened copper product composedessentially of a copper matrix through .which is dispersed a relativelysmall 3,552,954 Patented Jan. 5, 1971 amount of oxide of a readilyoxidized metal the oxide of Which has a high heat of formation, Whichcomprises heating to an elevated temperature a thin shape of an alloy ofcopper and said readily oxidized metal in the presence of an amount ofoxygen suflicient to oxidize all of said readily oxidized metal and tosaturate the residual copper matrix with oxygen, and continuing suchheating until said readily oxidized metal is substantially completelyconverted to oxide and the copper matrix is substantially saturated withoxygen. The resulting oxidized metal then is heated to an elevatedtemperature in a hydrogen-containing atmosphere until the oxygen dissolved in the copper matrix is substantially completely reduced and thecopper matrix has become severely embrittled. The resultinghydrogen-reduced product is comminuted, the comminuted metal is formedinto an extrusion billet, and said billet is coalesced by extrusion atan elevated temperature into a shape of desired cross section.

The alloy of copper and readily oxidized metal is preferably in thinsheet or strip form when subjected to oxidation, so that diffusion ofoxygen completely through it may occur in a reasonably short period oftime.

It is desirable to avoid over-oxidizing the copper alloy, andaccordingly it is preferable to limit the amount of oxygen availableduring the oxidation treatment. This can be accomplished, for example,by supplying the oxygen in the form of a controlled amount of copperoxide, with which the alloy is in intimate contact while it is beingheated during the oxidation step. During such heating, the copper oxidedissociates and the oxygen thereof diffuses through the copper. Theamount of copper oxide present should of course supply the amount ofoxygen required for internally oxidizing the readily oxidized metalcomponent of the alloy and substantially saturating the copper matrixwith dissolved oxygen.

The copper oxide can be provided separately from the alloy, or it can beprovided by surface-oxidizing the alloy in air until a scale of copperoxide has formed thereon to the requisite extent. The resultingsurfaceoxidized metal is then further heated in an inert atmosphereuntil the readily oxidized metal has become substantially completelyoxidized and the copper matrix has become substantially saturated withdissolved oxygen.

Alternatively, the amount of oxygen supplied may be limited byconducting the internal oxidation operation in a closed chamber in whichthe atmosphere initially contains about the right amount of free oxygento oxidize the readily oxidized component of the alloy and to saturatethe copper matrix.

The oxidation operation is preferably carried out at a temperature inthe range of 1400 F. to 1700 F. Lower temperatures can be used, but thetime required to complete the oxidation treatment is then greatlyincreased.

Higher temperatures also may be used, with some reduction in the timerequired for to complete formation of the oxide, but close temperaturecontrol is then necessary to avoid local overheating which might resultin partial or incipient fusion of the metal.

The hydrogen reduction of the metal after it has been subjected to theoxidation step may be carried out in any conventional heat-treatmentfurnace designed for maintaining a controlled atmosphere in contact withthe metal. The hydrogen content of the atmosphere may be supplied in theform of commercially pure hydrogen, or it may be supplied in the form ofany hydrogen-containing reducing gas, such as cracked ammonia, reformednatural gas, or producer or Water gas. Preferably a faily high hydogencontent is desirable in the furnace atmosphere during the reductionoperation, so that elimination of the excess oxygen proceeds rapidly.

The hydrogen reduction, like the oxidation operation, is preferablycarried out at a temperature in the range from 1400 F. to 1700 F.Temperatures below 1400 F. may be used successfully, but the timerequired for the reduction operation to be completed increases rapidlyas the temperature is decreased. Also, higher temperatures than 1700 F.may be used, but necessitate close temperature controlled to avoidlocalized melting or incipent fusion of the copper.

Hydrogen diffuses rapidly through hot metallic copper, and rapidlyeliminates oxygen dissolved therein. However, it does not readily reducemetal oxides having high heat of formation, such as are produced byinternal oxidation of the initial alloy, at temperatures below themelting point of copper. Consequently no great difficulty is encounteredin eliminating the dissolved oxygen from the copper matrix whileretaining the dispersed metal oxide that has been formed by thepreceding internal oxidation of the starting alloy.

It has been long known that when copper containing dissolved oxygen isreduced with hydrogen, the metal becomes embrittled. Variousexplanations of this phenomenon have been advanced; but whatever thereason may be, the degree of embrittlement becomes generally more severethe greater is the oxygen content prior to reduction. In the process ofthe present invention, advantage is taken of this embrittlement. Infact, it is desirable that the copper be substantially saturated withdissolved oxygen prior to hydrogen reduction, so as to effectsubstantially maximum embrittlement of the metal as a result of suchreduction.

The reduced embrittled metal, in accordance with the invention, ismechanically broken up into pieces small enough to be handled as agranular material. Such comminution may be effected in various ways, forexample, it can be accomplished in a hammer mill, or by subjecting theembrittled strip to a rolling operation. Any other procedure forsubjecting the metal to mechanical stress can also be used for reducingit to small particles.

The comminuted metal is next formed into a billet for hot extrusion. Itis possible to form such billet by compacting and sintering the granularmetal at a temperature approximating 1500 F. to 1800 F.; but a generallysimpler and preferred procedure is to can the granular metal in a sheetcopper container of the correct size for charging into an extrusionpress.

The resulting billet, however formed, is subjected to hot extrusion in aconventional extrusion press, at conventional copper extrusiontemperatures (for example, from 1700 F. to 1900" F.). The hot extrusionoperation converts the granular copper of the billet into a dense,homogeneous, extruded copper shape of whatever cross section has beenselected. For example, the billet may be extruded in the form of acopper rod, bar, tube or other conventional shape. The hot extrusionoperation has the effect of converting the embrittled metal to ductileand workable form, without, however, altering its character as atwo-phase product comprising a copper matrix through which particles ofthe metal oxide are dispersed. It thus retains its character as adispersion hardened material; yet it is free from embrittlement and maybe worked mechanically to a smaller cross sectional area or may beotherwise formed by a plastic deformation operation. In fact, such coldworking of the extruded shape to finished form is generally preferred.The metal may be subjected to intermediate anneals during such workingto restore workability lost by work hardening of the copper matrix; andit may be subjected to a final anneal to relieve work hardeningstresses.

Various readily oxidized metals having oxides of high heats of formationmay be used in preparing the alloy from which the internally oxidizedcopper product of this invention is made. Among such metals are, forexample,

4 beryllium, aluminum, magnesium, zirconium and silicon. Combinations ofsuch metals also may be used. The amount of such metal or metals presentin the alloy is generally in the range from 0.01 percent to 1 percent byweight of the alloy. A particularly advantageous alloy to be treated inaccordance with the invention is composed essentially of 0.05 percent to0.10 percent by weight beryllium and the balance commercially purecopper. The beryllium of such alloy is substantially entirely convertedto a beryllium oxide (beryllia) by the internal oxidation treatmentdescribed above.

The invention is exemplified below:

EXAMPLE 1 A solid solution alloy composed of 0.1 percent by weightberyllium and the balance commercially pure copper in the form of arolled sheet 0.02 inch thick, was packed in a closed heating chamber inintimate contact with cuprous oxide in sufficient amount to supplyenough oxygen by dissociation to completely oxidize the berylliumcontent of the alloy and to saturate the copper matrix. The pack washeated for six hours at 16000 F. The pack was then cooled to roomtemperature, the oxidized strip was removed from the pack, and thesurface of the strip was cleaned mechanically. The oxidized strip wasthen introduced into a controlled-atmosphere heattreatment furnacewherein it was heated in an atmosphere of commercial hydrogen at 1600 F.for six hours. At the conclusion of the treatment the strip was cooledto room temperature (under non-oxidizing conditions) and was found to bevery brittle. The brittle strip was comminuted in a hammer mill to theform of small granular particles. These particles were utilized to filla cylindrical container made of thin sheet copper, 3% inches indiameter, to form an extrusion billet. This billet was heated to 1800F., and at such temperature was extruded into the form of a round rod0.875 inch in diameter. The resulting rod was found to be free frombrittleness and capable of being plastically deformed without physicalinjury. The extruded rod was cold drawn, without intermediate anneals,to a wire 0.100 inch in diameter. The drawn wire was stress relieved at1300 F. for 1 /2 hours, and its physical properties were then determinedat 68 F. and at 1600 F. with the following results:

At 68 F. At 1,600 F.

Electrical conductivity, percent I .A. C .S. 21

EXAMPLE 2 A strip of the alloy of Example 1 was formed into an opencoil, with space between the turns, and the coil was heated in air at1300 F. for 2 hours in order to forni a light copper oxide scale on thesurface of the sheet. The resulting surface-oxidized coil was furtherheated in a nitrogen atmosphere at 1600" F. for 6 hours. As a result ofthis treatment, the oxygen of the surface scale diffused through themetal, saturating the copper matrix and internally oxidizing theberyllium to beryllium oxide. The thus-oxidized strip was then reducedin a hydrogen atmosphere and further treated as described in Example 1,with similar results.

EXAMPLE 3 A strip of the alloy of Example 1 was formed into an open coilas in Example 2 and was heated for 6 hours at 1600 F. in a closedchamber containing a measured amount of oxygen gas sufficient to convertthe beryllium of the alloy to beryllium oxide and to saturate the coppermatrix with oxygen. Following such oxidation treatment, the coil wasreduced in a hydrogen atmosphere and furttlier processed as described inExample 1, with similar resu ts.

The coalesced extruded products of Examples 1, 2, and 3 are not thensusceptible to hydrogen embrittlement since all dissolved oxygen in thematrix has already been gettered.

What is claimed is:

1. A method of making a wrought, ductile internally oxidized, dispersionhardened copper product composed essentially of a copper matrix throughwhich is dispersed a relatively small amount of oxide of a readilyoxidized metal the oxide of which has a high heat of formation, whichcomprises (a) heating to an elevated temperature a thin shape of analloy of copper and said readily oxidized metal in the presence of anamount of oxygen suflicient to oxidize all of said readily oxidizedmetal and substantially to saturate the residual copper matrix withoxygen.

(b) continuing such heating until said readily oxidized metal issubstantially completely converted to oxide and the copper matrix issubstantially saturated with oxygen,

(c) heating the resulting oxidized metal to an elevated temperature in ahydrogen-containing atmosphere until the oxygen dissolved in the coppermatrix is substantially completely reduced and the copper matrix hasbecome severely embrittled,

(d) comminuting the resulting hydrogen-reduced product,

(e) forming the comminuted metal into an extrusion billet, and

(f) coalescing said billet by extrusion at an elevated temperature.

2. The method according to claim 1, in which the alloy of copper andreadily oxidized metal is subjected to oxidation in sheet form.

3. The method according to claim 1, in which the alloy of copper andreadily oxidized metal is oxidized by heating it in a closed chamber oncontact with a sufiicient quantity of copper oxide to furnish bydissociation the amount of oxygen required by the oxidation operation.

4. The method according to claim 1 in which the alloy of copper andreadily oxidized metal is heated in air until a scale of copper oxidehas formed on the surface thereof, and the resulting surface-oxidizedmetal is then further heated in an inert atmosphere until the readilyoxidized metal has become substantially completely oxidized and thecopper matrix has become substantially saturated with dissolved oxygen.

5. The method according to claim 1, in which the alloy of copper andreadily oxidized metal is oxidized by heating in a closed chamber in anatmosphere initially containing just sufi'icient free oxygen to oxidizeall the readily oxidized metal and substantially to saturate theresidual copper matrix with oxygen.

6. The method according to claiml in which the oxidation of the alloy iscarried out at a temperature in the range from 1400 F. to 1700 F.

7. The method according to claim 1 in which the hydrogen reduction ofthe oxidized metal is carried out at a temperature in the range from1400 F. to 1700 F.

8. The method according to claim 1 in which the hydrogen-reduced andcomminuted metal is compacted and sintered to form a cohesive extrusionbillet.

9. The methd aoccording to claim 1 in which the hydrogen-reduced andcomminuted metal is packed in a copper can to form an extrusion billet.

10. The method according to claim 1 in which the initial alloy iscomposed of 0.01% to 1% by weight of readily oxidized metal and thebalance commercially pure copper.

11. The method according to claim 1 in which the readily oxidized metalof the initial alloy is selected from the group consisting of beryllium,aluminum, magnesium, zirconium and silicon.

12. The method according to claim 1 in which the billet of comminutedembrittl-ed metal is extruded at a temperature in a range from 1700 F.to 1900 F.

13. The method according to claim 1, in which the coalesced extrudedmetal is cold worked to finished shape.

14. The method of making a wrought, ductile dispersion hardened copperproduct composed essentially of a copper matrix through which isdispersed a relatively small amount of beryllia, which comprises (a)heating to temperature in the range from 1400 F. to 1700 F. a thin shapeof a beryllium-copper alloy composed essentially of 0.05% to 0.25%beryllium and the balance commercially pure copper in the presence of anamount of oxygen sutficient to oxidize substantially the entireberyllium content of said alloy and substantially to saturate theresidual copper matrix with oxygen,

(b) continuing such heating until substantially all the beryllium of thealloy is oxidized to beryllium oxide and the copper matrix issubstantially saturated with oxygen,

(c) heating the resulting internally oxidized metal to a temperaturebetween 1400 F. and '1700" F. in a hydrogen-containing atmosphere untilthe oxygen dissolved in the copper matrix is substantially completelyreduced and the reduced metal product has become severely embrittled,

(d) comminuting the resulting embrittled product,

(e) forming the comminuted product into an extrusion billet, and

(f) coalescing said billet by extrusion at a temperature in the rangefrom11700 F. to 1900 F.

References Cited UNITED STATES PATENTS 3,026,200 3/ 1962 Gregory 75-206X 3,070,440 12/1962 Grant --206 3,434,830 3/1969 Grant 75206 CARLD. QUARFORTH, Primary Examiner A. J. STEINER, Assistant Examiner US. Cl.X.R.

